The present invention relates to an oscillating type compressor suitable for use to compress a fluid, for example, air.
As an oilless enclosed reciprocating compressor for compressing air or other fluid, there is commonly known an oscillating type compressor having an oscillating type piston reciprocating in a cylinder while oscillating (for example, see Japanese Patent Application Publication No. 2003-161260). In such an oscillating type compressor, a piston is connected to a crankshaft, and the crankshaft is driven to rotate by using a motor. The piston has a lip ring attached to the outer periphery thereof to serve as a seal member.
In the above-described oscillating type compressor according to the related art, when the piston reciprocates in the cylinder while oscillating, not the whole periphery of the lip portion of the lip ring but only a part thereof that is located at the load side during the compression stroke is strongly pressed against the inner peripheral surface of the cylinder and thus becomes worn.
That is, during the compression stroke where the piston moves from the bottom dead center to the top dead center, the pressure in the compression chamber becomes high, so that the piston and the lip ring are subjected to a large load. Further, of two regions of the lip ring at two opposite ends in the oscillation direction of the piston, one region that is displaced to a larger extent during the compression stroke until the top dead center is reached serves as a load side region that is subjected to a larger load. Accordingly, partial wear occurs at the load side region of the lip ring. During a continuous operation of the compressor, in particular, the cylinder and the lip ring are heated to a high temperature by heat of compression from the compression chamber, frictional heat and so forth. Therefore, the wear of the lip ring is accelerated.
Consequently, the lip ring may become incapable of sealing due to the wear at the above-described one part thereof although the rest of the lip ring has become worn to only about 30 percents of the thickness thereof. Moreover, the lip ring is fixedly fitted to the disk portion of the piston to prevent leakage of air from the compression chamber. Therefore, when the oscillating type compressor is operated, wear occurs concentratedly at one part of the lip portion that is located in the oscillation direction of the piston. Accordingly, the service life of the lip ring is unfavorably dependent on the wear at the one part thereof.